Composite blocks of adsorptive material, such as adsorbent activated carbon, and polymeric binders, such as ultra high molecular weight polyethylene (UHMW PE), are useful in water filter technology. Carbon block technology, for example, provides comparable functionality of loose bed carbon particles, for example, removal of organic contaminants from water, without the mess or taking up too much space.
As is known to those skilled in the art, THMs (trihalomethanes) are a common contaminant in drinking water, being formed by the reaction of chlorine (used for disinfection) with naturally occurring organic matter in water. THMs are suspected carcinogens and also can impart taste and odor to water. Another common drinking water contaminant is methyl t-butyl ether (MTBE), a water-soluble gasoline additive. Removal of THMs, MTBE, and other VOCs from drinking water is typically accomplished by physical adsorption on activated carbon. However, the capacity of activated carbon for THMs, MTBE, and similar VOCs is lower than presently designed. For example, capacity data published by the US EPA (Dobbs, 1980) for chloroform on activated carbon is only 0.012 g/100 g at 15 ppb.
Water filters used in the prior art for removal of THMs commonly employ carbon blocks, manufactured by binding smaller activated carbon particles with a binder such as polyethylene. The design of carbon blocks for water filters for consumer applications is driven by the need for carbon blocks to have a relatively small physical size. The use of smaller carbon particles has in the past allowed blocks to be made small, while maintaining the kinetics required for removal of contaminants. Therefore, the removal of THM and VOCs by carbon blocks has been limited by equilibrium adsorption capacity.
Prior art for maximizing performance for THM and VOC have tended to use activated carbons with surface areas above a minimum value. For example, Toshiro (JP7215711) discloses a method for THM removal based on an activated carbon with surface area >1500 m2/g. In another example, Tsushima et al. (JP00256999) disclose a water purifier for THM employing an activated carbon with surface area greater than 1300 m2/g. Because the process of activating carbon involves removing carbon atoms to create pores and internal surface area, higher surface area carbons have lower densities than lower surface area carbons made from the same raw material.
It is desirable to provide water filters having increased capacity for THMs and trace VOCs in a small carbon block. This is done by maximizing the capacity of activated carbon used in a block on a per volume basis and by maximizing the amount of carbon in a composite carbon block (by minimizing the binder content).
There is an on-going need to increase capacities for contaminants in water filter media. Further, there is a need to reduce the amount of binder needed in these filters.